Agriculture Reference
In-Depth Information
Table
Leaf area on short shoots as a percentage of the total
leaf area of mature apple trees of 'Cox's Orange Pippin'/'M.
.
'
Pruning
Cropping trees
Non-cropping trees
Light
.
.
Heavy
.
.
From Barlow ( ). Reproduced with permission.
spur leaves emerge before full bloom. After flowering some secondary leaves
may develop on the spurs and their development is usually complete about a
month after full bloom.
The other leaves develop on the new shoots, i.e. on terminal, lateral and
bourse shoots. Proctor and Palmer (
) found that at full bloom true spur
leaves made up
% of that
of 'Golden Delicious', the balance being bourse shoot leaves. At maturity the
ratio of spur leaves to new shoot leaves is very variable. Barlow (
% of the leaf area of the spurs of 'Cox' but only
) found
that the proportion of the leaf area borne on short shoots (spurs) was reduced
by heavy pruning and the absence of crop (Table
), i.e. by treatments which
promote extension shoot growth. The treatments in this trial were extreme,
giving something near to the maximum range of spur to shoot leaf ratios for
mature trees. Palmer and Jackson (
.
) found
-
% of the leaf area of
'Golden Delicious'/'M.
' pruned as slender spindle bushes to be spur leaves.
Wunsche
et al.
(
) found the percentage of spur leaf area to range from
%
to
% of the total in a trial of different rootstocks and training systems with
'Empire'/'M.
'. The relative pattern of spur and shoot leaf development over
the season was well illustrated by Forshey
et al.
(
) working with 'MacSpur
McIntosh' (Figure
), who found that at the time of full canopy development
spur leaves made up more than half of the total leaf area, after having made
up a much larger proportion early in the season.
The number of leaves which develop on new shoots is a function of tem-
perature (Abbott,
.
): effects of
temperature under controlled environment conditions are shown in Table
; Johnson and Lakso,
; Lindhagen,
.
Leaf production is also influenced by many of the factors discussed in relation
to shoot growth. The number of leaves produced is reduced by water stress
and nutrient deficiencies and is under hormonal control. Tustin
et al.
(
.
)
showed that shading of spurs reduced the number of leaves produced on their
bourse shoots in the subsequent year as a result of the earlier cessation of
growth of these bourse shoots.
As discussed under shoot growth, the removal of expanding leaves can result
in a check to shoot growth followed by its prolongation and production of more
leaves than might otherwise have occurred (Abbott,
).
